For the power supply to mobile portable devices such as mobile telephones, portable computers and the like or else for the power supply to other devices or technical devices such as vehicles, batteries, in particular rechargeable batteries, are often used. In German, such rechargeable batteries are also referred to as accumulators (Akkumulatoren or Akkus, for short). Irrespective of the type of battery used and the type of device, it is in this case often desirable to inform the respective user of the device of the state of charge of the battery so that the user notices in good time before the battery is empty and can no longer supply sufficient current, for example, with the result that the user can replace and/or recharge the battery before the device fails, for example.
Usually, in some applications, the state of charge of the battery is determined by an open terminal voltage of the battery being measured, i.e. a voltage in a state in which no load or else a low load (for example during standby operation) is coupled to the battery, i.e. in a state in which there is in any case a low current load. In this case, however, there is the problem that, after the beginning of the state of low current load, sometimes several hours can elapse until the open terminal voltage reaches a steady state (i.e. relaxation has finished), which makes such measurements very difficult to implement in many situations since often the battery is coupled to a higher load again within this time, i.e. a higher load current needs to be provided, for example in order to provide device functions.
In order to achieve rapid estimation of the state of charge of the battery, the open terminal voltage can be measured a plurality of times during a relaxation operation and an estimated value for the open terminal voltage in the steady state can be determined by extrapolation from the multiple measurements. On the basis of this estimated value, the state of charge can then be determined. This provides sufficient accuracy for many applications. However, for some applications it would be desirable to shorten the duration during which values for the open terminal voltage are measured, wherein a desired accuracy of the determination of the state of charge is still intended to be ensured.